(a) Field of the Invention
The present invention relates to a shock absorber of an automotive suspension system, and in particular, to a hydraulic shock absorber capable of controlling a damping force thereof.
(b) Description of the Related Art
Shock absorbers are mounted between a vehicle frame and a suspension, and operate on the principle of forcing fluid through restricted openings on both extension strokes and compression strokes.
In general, a hydraulic shock absorber includes a cylinder filled with hydraulic fluid and a piston inserted into the cylinder. The piston consists of a piston rod and a plunger assembly which is slidably fitted into the cylinder so as to divide the inside of the cylinder into two compartments. The plunger assembly is provided with a main orifice and a bypass orifice which provide communication between the two compartments in the cylinder, and the orifices have respective valve mechanisms for controlling the amount of fluid communication.
FIG. 5 shows a prior art shock absorber capable of adjusting damping force thereof. As shown in FIG. 5, the shock absorber comprises a cylinder 112 connected to a suspension (not shown) and a piston 114 inserted into the cylinder 112, with an end of piston 114 outside the cylinder 112 being connected to a vehicle body (not shown). The piston 114 includes a cylindrical piston rod 115 and rotary valve 124 slidably fitted in the cylinder 116. In a space inside the piston rod 115 with chamber 126, a step motor 122, gear mechanism 120, and clutch are located such that the rotary valve 124 receives rotary torque from the step motor 122 by way of a control rod 118 connecting the gear mechanism 120 to the clutch. Also, upper and lower chambers divided by the rotary valve 124 communicate through orifices 119 formed in a valve case, and the amount of fluid 128 passing through the orifices 119 can be adjusted by rotating a valve plate which varies the size of the orifices according to the amount of rotation of the step motor 122. Accordingly, the damping force of the shock absorber can be adjusted as needed.
However, since this shock absorber uses complicated mechanical structures such as a motor, gear mechanism, clutch, and so forth, there are difficulties in design, and it is impossible to precisely adjust the damping force.
Furthermore, the complicated mechanical structure delays response time of adjustments to the damping force on an uneven road.